The present invention relates to plasma processing apparatus, and more particularly to such apparatus that process semiconductor wafers, using controlled plasma.
Circuit patterns have recently traced the course of becoming detailed, because of the high integration of semiconductor devices. The processing size in demand is becoming even tougher. In addition, besides the fact that enlarging the size of the diameter of wafers is underway for the purpose of improving productivity, the application of new materials and the modification of wiring structures are being considered, to improve the performance of the elements. In keeping with these new technologies, the development of a new processing technology is underway. However, the development of this processing technology is extremely difficult and costly.
Under these circumstances, even though the same process were to be executed vis-à-vis each respective wafer, using similar types of manufacturing devices, problems such as mechanical differences in the devices causing discrepancies in processing results, and aging, as the number of wafers being processed with the same manufacturing device increases, causing changes in processing results is growing. These problems consequently are extremely serious, because they will bring about decreased operational rates in the devices, reduced yields due to mixture of foreign matter, and an extended period of, as well as increased cost in, the development of processing technology.
An apparatus that processes wafers, using plasma, for example, a plasma etcher or a plasma CVD, among the semiconductor manufacturing apparatus, solves the problems by monitoring the plasma state on a display device, controlling various parameters based on the monitored result, and further controlling the result of the processing. In constructing and monitoring the manufacturing process as just mentioned, it is very important to especially grasp the characteristic of the plasma and more particularly information on the electron density and temperature of the plasma.
In the measurement of plasma characteristic in a prior-art processing apparatus and/or method using plasma, a measuring method using electromagnetic waves with the aid of a microwave interferometer and Langmuir probe method have been used.
The microwave interferometer has a pair of windows each provided in a respective one of a pair of opposite walls of an container in which plasma is being produced. A microwave is entered through one of the pair of windows into the container, a microwave outgoing from the other window is detected, and an electron density is calculated based on the difference in phase between the incident and outgoing microwaves.
In the Langmuir probe method, a small metal probe (electrode) is inserted into and exposed to the plasma and a DC bias voltage and a high frequency voltage are applied to the probe. A resulting change in the current is used to calculate the electron density and temperature.
In the measuring methods using electromagnetic waves, the device used is complicated and difficult to handle. That is, use of a large-scaled expensive device and difficult adjustment of the microwave transmission path are required. Furthermore, the windows for the incident and outgoing microwaves are required to be clean in order to acquire a required accuracy of the measurement.
In the Langmuir probe method that requires insertion of the electrode into the plasma, pollution of the wafers to be processed with the electrode material and deposition of an insulating film on a surface of the probe make the measurement impossible. Thus, a long-time measurement is impossible. Since there is a high probability that foreign matters produced from the probe construct will reduce the yield, the Langmuir probe method has not been used in the manufacturing site, like the electromagnetic method. In an apparatus that uses a capacitively coupled plasma source, a high frequency field intensity in the plasma is very high. Thus, the probe method cannot be used because the voltage-current characteristic of the probe is disturbed by the high frequency field, which cannot make accurate measurement.
Recently, measuring methods that have conquered these drawbacks as far as possible have been developed. A typical measurement method is disclosed in JP-A-8-222396, wherein the plasma characteristic is measured by an electrode attached to a wall. This method is to calculate the electron density from a series resonance frequency produced in the plasma in accordance with the principle of a self excited electron plasma resonance spectroscopy. Another typical method is a high frequency probe method disclosed in JP-A-2000-100599. In this method, an electrode covered with an insulator radiates high frequencies into plasma, and a particular high frequency that is absorbed to a maximum by the plasma is obtained based on a high frequency characteristic of those reflected waves from the plasma. The electron density is then calculated based on the particular high frequency.
However, those new measuring methods also have problems. In the self-excited electron plasma resonance spectroscopy disclosed in JP-A-8-222396, the sensor is attached to the wall of the container within which the plasma is to be produced. Thus, resulting information on the plasma represents an average electron density present between the plasma container wall and the high frequency radiator. In the processing using the plasma, the processing performance is determined depending on what plasma is produced near the discharge electrodes that produces the plasma or as a result how the plasma characteristic is near the workpiece. Thus, information on the processing state is reduced at the average electron density.
The method disclosed in JP-A-2000-100599 has a merit that continuous measurement is possible even when an insulating film is deposited on the surface of the sensor. It, however, still has the drawback that information on the plasma near the workpiece is difficult to obtain. This is because when the probe is brought close to the workpiece, the probe itself will disturb the plasma characteristic to thereby prevent normal processing, and because a film deposited on the probe surface is separated to become foreign substances to the workpiece to thereby prevent normal processing and reduce the yield. As a result, the probe cannot be inserted around the workpiece in the apparatus in the manufacturing line.
The present invention has been made in view of the above problems. It is an abject of the present invention to provide a plasma processing apparatus free from the problems with the prior art.
Another object of the present invention is to provide a plasma processing apparatus capable of acquiring information on the state of plasma near a workpiece, for example, information on at least one of the electron density and temperature of the plasma, without inserting a special sensor into the plasma around the workpiece.
A further object of the present invention is to provide a plasma processing apparatus that controls the working process based on acquired information on the plasma state.
In order to achieve the above objects, one aspect of the present invention, a plasma processing apparatus comprises: a body that comprises a vacuum processing chamber that contains a wafer stage on which a semiconductor wafer is held, a plasma producing unit for producing plasma within the vacuum chamber, and a high frequency source for applying a high frequency bias voltage to the wafer stage; and a control unit for controlling various parameters of the body of the plasma processing apparatus, the control unit comprising a detecting unit for detecting the high frequency voltage or high frequency current applied from the high frequency source to the wafer stage or for calculating a difference in phase between the detected high frequency voltage and current.
According to another aspect, the electron density and temperature of the plasma is calculated based on the detected high frequency voltage, the detected high frequency current, and the obtained difference in phase between the high frequency voltage and the high frequency current to thereby control the body of the plasma processing apparatus.